The Hennepin County Medical Examiner released the cause of death for two victims in Wednesday's explosion at Minnehaha Academy.
A memorial service for Carlson, a part-time janitor known for giving students ice cream treats, is scheduled for Sunday at the school.
The National Transportation Safety Board has started its investigation into a natural gas explosion that killed two people at a Minneapolis school. The blast ignited a fire and caused a portion of a school building to collapse.
Federal investigators were taking a closer look at the wreckage of a Minneapolis school on Friday after a natural gas explosion sent part of a building crashing down, killing two school employees and injuring at least nine others.
The National Transportation Safety Board is investigating.
Two other adults remained hospitalized Thursday in satisfactory condition.More news: Asta italiana per Emre Mor
The school described Carlson, 82, as its "biggest cheerleader".
"We're going to get through it", said Minnehaha Academy President Donna Harris, who was injured in the explosion. Minnehaha Academy said the explosion killed Ruth Berg, the school's receptionist for 17 years. The blast affected Minnehaha Academy's "upper school", which houses the high school. The company had no immediate comment on Friday but said in a statement to local media on Thursday that its employees were among the injured. City fire officials said the situation would have been far worse if pupils were in class. The school earlier said longtime receptionist Ruth Berg died in the blast, and that janitor John Carlson was missing.
The local medical examiner says the two people who were killed during an explosion at a Minneapolis school died from blunt force injuries sustained when part of a building collapsed.
It was not damaged in Wednesday's blast.
The private Christian school serves students from pre-kindergarten through 12th grade. At a news conference Wednesday night, Fruetel didn't specify whether Carlson's body was the one that was located.
Jenny O'Brien, spokeswoman for the state agency, said such violations were considered routine.